This invention relates to a metal capped piston having insulation under the cap. In particular, it relates to a brake piston made from a thermosetting molding compound that has a molded-on metal cap under which is insulation.
Brake pistons are commonly made by molding phenol formaldehyde molding compound into the shape of the piston, then grinding the rough piston to the precise piston dimensions. Metal caps are often molded onto the top of the piston to prevent degradation of the phenolic from the heat generated in braking. While a metal cap will extend the life of a piston, the phenolic material under the metal cap will eventually degrade, resulting in the failure of the piston.